The technology disclosed herein generally relates to optical fiber networks that enable communication between electrical components. In particular, the technology disclosed herein relates to electrical avionics systems interconnected by an optical avionics data bus.
The use of optical fiber cables instead of electrical wiring for a high-speed avionics data network may result in significant reduction of weight, cost, electromagnetic effects, and complexity of electrical wiring integration. In modern aircraft, line replaceable units (LRUs) (such as avionics computers and sensor units) typically include a housing containing a transceiver to enable optical fiber communication with other LRUs. An optical connector on the LRU housing enables an external optical fiber cable to be connected to the LRU.
More specifically, each LRU connected to an optical avionics data bus typically includes an optical-electrical media converter) having an electro-optical transmitter and an opto-electrical receiver (hereinafter collectively referred to as an “optical-electrical bidirectional transceiver”) to enable optical fiber communication with other LRUs. The electro-optical transmitter converts electrical signals into optical signals; the opto-electrical receiver converts optical signals into electrical signals. An optical connector on a housing of the LRU enables an optical fiber cable to be connected to the LRU.
In legacy avionics fiber optic systems, non-pluggable small form factor optical-electrical bidirectional transceivers (hereinafter “SFF transceivers”) are used inside the LRU of the legacy avionics systems. But the current trend in the optical fiber industry is to gradually discontinue use of non-pluggable SFF transceivers and replace them with small form factor pluggable optical-electrical bidirectional transceivers (hereinafter “SFP transceivers”). As used herein, the term “pluggable”, when used as an adjective to characterize a capability of a first component, means that the component may be coupled to and later uncoupled from a second component by inserting male portions (e.g., pins or plugs) of one of the first and second components into respective female portions (e.g., receptacles or sockets) of the other of the first and second components.
Many modern fiber optic communication system upgrades, new technology and new design features are no longer implemented using SFF transceivers in the industry. Commercially available SFP transceivers have advanced features built-in for modern fiber optic communication systems, including digital diagnostic monitoring and built-in testing. Also because the SFP transceiver is a widely accepted package format in the fiber optic industry, the cost of the SFP transceiver is very low due to the economy of scale. This industrial trend in the development of transceivers creates a problem when deploying new optical fiber systems in avionics platforms. For example, SFP transceivers need to be deployed in many LRUs of these new avionics optical fiber systems.
Some legacy avionic optical fiber systems use SFF transceivers which have a 10-pin (2×5) dual-in-line package format that allows the SFF package to be soldered permanently on the LRU printed circuit board (PCB) without concern for detachment due to vibration. But the currently popular SFP transceiver package has no solder pins and is designed to be pluggable into a 20-pin socket mounted on a PCB. Therefore, the transceiver is not permanently attached to the PCB. While this SFP design is acceptable for use in non-avionics environment, this design is not acceptable for avionics platforms due to concern over detachment of the SFP transceiver under vibration and also corrosion of the SFP transceiver's contact pads due to exposure to moisture and humidity.
One possible response to the above-described challenge is to fabricate customized SFP transceivers for different avionics platforms using hermetic transceiver packages. This course of action would be expensive. Also finding suppliers capable of making hermetic SFP packages may be challenging because hermetic package format is not part of the multi-source agreement for SFP transceivers in the fiber optic industry. One prior solution for partially ruggedizing an SFP transceiver involved simply depositing a conformal coating on the PCB of the SFP transceiver, but did not include soldering the SFP transceiver to the PCB of an LRU.